To seal off rotating systems, non-contact seals, in particular labyrinth seals, are widespread in turbomachine construction. In the separating gap, through which flow occurs, between rotating and stationary parts, high friction power occurs as a result of the forming flow boundary layers. This leads to heating of the fluid in the separating gap and thus also to the heating of the components surrounding the separating gap. The high material temperatures result in a reduction in the service life of the corresponding components.
DE 195 48 852 A1 discloses a radial compressor of simple construction without a sealing geometry formed in the separating gap. In this case, too, the friction heat produced as a result of flow shearing layers at the rear wall of the compressor impeller causes heating of the compressor impeller and thus reduces its service life.
EP 0 518 027 B1 discloses air cooling for radial compressors with a sealing geometry on the rear side of the compressor impeller. To this end, an additional annular space is formed between the individual sealing elements the casing wall side of the radial compressor. A cold gas which has a higher pressure than the pressure prevailing at the outlet of the compressor impeller is directed into this annular space. The air supplied acts as impingement cooling. In the process, it divides in the sealing region and flows mainly radially inward as well as outward. This is intended to additionally achieve a blocking effect against the flow of hot compressor air through the separating gap from the outlet of the compressor impeller. However, the air blown in in this way causes an increase in thrust and additional friction losses in the flow boundary layers.
In addition to this direct cooling, DE 196 52 754 A1 also discloses indirect cooling of the rear wall of the compressor impeller or of the medium flowing through the separating gap. To this end, a feed and distributing device connected to the lubricating-oil system of the turbocharger is arranged on or in the casing part disposed at the rear wall and forming with the latter the separating gap. The oil used for the bearing lubrication serves as cooling medium, for which purpose the lubricating-oil circuit of the turbocharger is tapped. A disadvantage of this cooling is the relatively high oil demand and the heat quantity to be additionally dissipated by the oil cooler. This leads to an increased overall volume of the cooler. In addition, in the event of an accident with damage to the corresponding parts, there is an increased risk of deflagration.
U.S. Pat. No. 4,815,184 also discloses water cooling of the bearing housing of a turbocharger. However, this cooling serves to remove the carbonization risk of the lubricating oil remaining in the bearing housing of the turbocharger after shutdown of the latter. In contrast to the abovedescribed solutions of the prior art, the feeding of the cooling medium is not necessary during the continuous operation but rather when the turbocharger is shut off. This type of cooling of the bearing housing is therefore unable to provide any reference to indirect cooling of the flow in radial gaps formed between rotors and stators of turbomachines. In addition, this solution expressly does not deal with the cooling of the intermediate wall.